Exosomal SpFlotillin-1 participates in resistance to Vibrio parahemolyticus infection in mud crab (Scylla paramamosain)

Exosomes have been considered anti-microbial immune factors in animals (including aquatic animals). However, the relationship between exosomal proteins and immune responses during bacterial infection has not been addressed. Flotillin-1 has previously been shown to enrich plasma membrane which implicates in cellular processes, including signal transduction, membrane trafficking, and molecular sorting. In this study, SpFlotillin-1 was cloned and characterized from mud crab (Scylla paramamosain). SpFlotillin-1 was found to be up-regulated in the hemocytes of mud crabs after infecting with V. parahaemolyticus. RNAi knockdown of SpFlotillin-1 showed capacity in suppressing phagocytosis and reducing the expression of antimicrobial peptides (AMPs) but increasing the ROS production in hemocytes. Furthermore, SpFlotillin-1 densely packaged in the exosomes can regulate the phagocytosis, expression of AMPs through MAPK and NF-kappa B pathway, and production of ROS, eventually activating the immune response to bacterial infection in mud crabs. Taken together, the results of this study provide a new finding on the mechanism that exosomal SpFlotillin-1 may participate in the V. parahaemolyticus infection through the regulation of phagocytosis and activation of AMP synthesis in mud crabs.